1. Field of the Invention
The present invention relates to a digital camera designed to be capable of capturing a freeze-frame picture of celestial bodies in long-exposure astrophotography, and more specifically, relates to a digital camera that is designed to make long-exposure tracking astrophotography possible.
2. Description of the Related Art
If long-exposure astrophotography is carried out with a fixed camera, added light of stars during a long exposure form straight or curved light trails since celestial objects move relative to the camera due to the earth's rotation (diurnal motion). To carry out a long exposure in order to photograph a celestial body so that the celestial body appears to be still (stationary) relative to a photosensitive film or an image sensor (image pickup device), an equatorial equipped with an auto-tracking system is generally used.
In recent years, a method of obtaining a still image of celestial bodies such as planets and stars in long-exposure astrophotography has been proposed in which a celestial body (or bodies) is photographed a plurality of times with a fixed digital camera without using an equatorial, and thereafter, the images thus obtained at the plurality of times are added while correcting the positions of the celestial body (bodies) using data on the obtained images (see Japanese Unexamined Patent Publication Nos. 2006-279135 and 2003-259184).
The assignee of the present invention has proposed an image shake corrector which detects camera shake with a gyro sensor to compensate for not only vibrations in vertical and horizontal directions but also rotational vibrations by moving an image sensor in any given directions orthogonal to an optical axis and rotating the same image sensor about an optical axis (see Japanese Unexamined Patent Publication 2007-25616).
However, an equatorial equipped with an auto-tracking system is generally expensive, heavy and difficult to handle. The type of digital camera (disclosed in Japanese Unexamined Patent Publication Nos. 2006-279135 and 2003-259184) which synthesizes a plurality of images has inferior image registration accuracy and has a slow image processing speed, thus such problems occur while performing tracking astrophotography using only such a type of digital camera.